This invention relates to instruments for distance measurement, such as rangefinders.
Presently, an array of laser rangefinders of different applications is known. An example of one such rangefinder is described in “Systems for optical detection and ranging” by V. V. Molebny (Mashinostroenie, Moscow, 1981, p. 52); and is used to determine distance to an object with range discrimination. It utilizes a pulse laser with an optical collimation system emitting short optical pulses toward the object; exiting start reference pulse is diverted toward a photoreceiver with pulse amplification, which is connected to a start pulse of the time interval counter. The altered time interval, in either analog or digital form, reflects measured distance to the object.
Disadvantages of such laser rangefinder include inability to discriminate object by distance or field of view; e.g., of the field of view contains several objects, or a specular object, or a continuous object, it is not possible to select an object by its angular or reflective characteristics.
Above disadvantages are partly overcome by a pulse rangefinder (Ibid, p. 55, FIG. 2.6), a prototype of this invention.
Above rangefinder contains (connected serially) a pulse laser with an optical system, a pulse amplifier and a regulated pulse generator; also, serially connected, photoreceiver based on avalanche photodiode with an optical system (conjugate with that of the laser), an amplifier of photo detected signals, comparator, time-interval meter, and an object detection indicator. Information about distance to object is stored in a memory module from which information pertaining to a specific object can be retrieved by a reader device.
The objective was the construction of a compact laser rangefinder for detection of concealed surveillance on surveillance optical equipment (spyglasses, periscopes, binoculars, cameras, et cetera). The visual discrimination of above-mentioned objects against the background objects (walls, buildings, trees, grass, et cetera) was required both by reflective characteristics (quasi-cat's eye objects against diffuse objects) and by angular characteristics (specular objects against continuous objects).
To achieve this objective following is proposed: a laser rangefinder containing, serially connected, pulse laser with an optical system, a pulse amplifier and a regulated pulse generator; also, serially connected, a photoreceiver based on an avalanche photodiode with an optical system (conjugate to that of the laser), an amplifier of photo detected signals, comparator, time-interval meter, and an object detection indicator. Unique characteristics of the proposed rangefinder are: an additional output of the pulse amplifier, to which second laser with an optical system (conjugate to that of the first laser and avalanche photodiode) are connected; and a second input, which is connected to the first input of the pulse amplifier, first output of the regulated pulse generator and first input of the time-interval meter. Unique additions also include:                a synchronizer with its first output connected to the third input of the pulse amplifier, its third output connector to the third input of the first comparator, and its input connected to the second output of the regulated pulse generator;        a second comparator with its first input connected to the output of the amplifier of photo detected signals as well as to the first input of the first comparator, and its second input connected to the second output of the synchronizer;        first and second integrators with their inputs connected to the output of the second comparator;        a third integrator with its input connected to the second output of the synchronizer;        a summation counter with its first input connected to the output of the first integrator, its second input connected to the output of the second integrator, its third input connected to the output of the third integrator, and summation counter's output connected to the second input of the first comparator;        an avalanche photodiode power regulator with its first output connected to the second input of the summation counter and its output connected to the avalanche photodiode;        a regulated counter, installed in the interface of the first comparator and object detection indicator with the counter's first input connected to both output of the first comparator and to the second input of the time-interval meter, its second input connected to the fourth output of the synchronizer, and its first output connected to both the input of the object detection indicator and input of an additional “inhibit pulse” generator;        a strobe generator with its input connected to the second output of the regulated counter and its output connected to the input of the regulated pulse generator;        the output of the “inhibit pulse” generator is connected to the third input of the time-interval meter, while the output of the time-interval meter is connected to the fourth input of the pump pulse amplifier.        
Additionally, we propose to equip this laser rangefinder with a speech synthesizer installed on the interface between time-interval meter and pump pulse amplifier. The synthesizer's first input is then connected to the output of the time-interval meter, its second input—to the output of the “inhibit pulse” generator, and the synthesizer's output is connected to the fourth input of the pump pulse amplifier.
As a result of the modifications described above discrimination of the objects measured is increased. Introduction of three ways of regulation allows for adaptation of the detection threshold by (1) gradually changing factors—temperature and gradual background changes (daylight, night time, clouds, et cetera); (2) by rapidly changing factors (background change light/dark, building, shadow, random extraneous light source in the field of view during rapid scan), (3) by distance to object in order to decrease amplitude-temporal error due to distance change and space-time amplitude of discrimination of target objects (optical systems) from the extraneous objects (diffuse-reflective).
Utilization of the speech synthesizer would allow the operator to receive distance information without interruption of the search and observation process; this increases reliability and efficiency of information detection and recording. Employment of the object detection indicator allows rapid fixing the rangefinder's field of view on the object.
The dual pumping mode allows for better concealment and decreases the threshold of detection by night-vision gear. Utilization of two emission channels with separated emission diagrams allows for discrimination of target specular objects (optical systems) from diffuse objects (diffuse reflective walls, building windows, road signs, et cetera) by their angle and linear dimensions criteria.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.